The invention relates to a method for determining the viscosity of a fluid, as well as to a device for carrying out this method.
In flow mechanics, the phenomenon with which a body is arranged within a flow and with which counter-running vortices form therebehind in the flow direction, is called a Karman vortex street. If such a body is subjected to onflow with a low speed, then the flow runs in a laminar manner with a low Reynolds number. With an increasing speed (higher Reynolds number) first, stationary vortices are formed, which given an increase of the flow speed, detach and form a so-called vortex street behind the body. The detachment frequency of the vortices may be determined by way of the Strouhal number, which is dependent on the shape of the body. On account of the linear relation of the detachment frequency and the flow speed, this physical effect is utilized for the flow measurement with non-abrasive, low viscosity media. Such measurement arrangements are known as vortex flowmeters.
Such a vortex flowmeter is for example described in European Patent Publication No. 1 434 034 A 1. Such a vortex flowmeter is particularly applied in conduit systems of circulations, be it in the conduit itself or also within the pump producing the circulation. Such a measurement arrangement typically consists of a body projecting into the flow, the body being a so-called obstruction, and of a sensor arranged at a suitable distance therebehind, typically a pressure sensor, in particular a differential pressure sensor. Such components nowadays may be manufactured in an inexpensive manner and may determine the flow rate with a high accuracy.
With such conduit circulations, as are to be found, for example, in heating systems, in solar installations, in the cooling water circulation of a vehicle or likewise, the measurement of the flow speed is often not sufficient. In modern systems, all system variables which are significant for the operation should be detected in an as continuous and reliable as possible manner. It is therefore the object of the present invention to detect a further variable which is relevant for the operation of an installation, in particular with a vortex flow measurement device with as few as possible modifications.